1. Field of the Invention
This invention of a fluid automatic transmission for bicycles relates to several basic hydraulic devices, specifically the fluid couple, the common vane pump or motor and the simple torque-converter.
2. Background of the Invention
Classification: Bicycle, 280/216.000
Related classifications: Class 74, subclass 337, torque responsive reversing or ratio change; 74/730.1, gearing combined with a fluid force torque transmitting device to form a drive train; 74/665, single gearing unit includes a fluid drive; 74/393, transmission with varying speed ratio.
A basic torque-converter concept was the primary theoretical mode for this fluid automatic transmission (see FIG. 2 View 1), where a power input 6, is applied to a surface 4, connected with fluid to an output stator 2, FIG. 2, within a fluid chamber 9, and where the distance in fluid shear between the two View-AA, is controlled in response to changes in torque using springs 3a, thereby changing “slip” or step-down as a means to change mechanical advantage for the rider automatically.
Automatic bicycle transmissions currently available are in general gear shifting devices having torque sensing systems or gyroscopic control for torque or cadence, respectively, to move the chain from sprocket to sprocket as a transmission means. Fluid drives and devices have been designed to include the ability to change mechanical advantage without gearing and without rider input [Satao 1995, 5387000], these qualities defined as being essential to the operation and performance qualities of a fluid automatic bicycle transmission. This important patent by Sato embodies most of the underlying concepts of fluid drives and automatic transmissions.
However, previous automatic bicycle transmissions and fluid drives have significant drawbacks which prevent them from gaining the volume market in bicycles. A most important factor in order for the industry to adopt a fluid drive of any type is the need for the product to be a replacement part and not require any modification to a typical modern bicycle with multiple speed cassette or freewheel and some type of sifting device. Therefore, this fluid automatic bicycle transmission was intentionally designated to replace existing bicycle gearing of any standard type including single-speed freewheel replacement, cassette of sprockets replacement, cassette freehub body replacement, standard freewheel multi-speed replacement (see FIGS. 5A–D). Also, these same parts are functionally applied internally to the hub body for the embodiment (see E, FIG. 5, FIG. 16) that replaces existing hubs.
The concept of an automatic transmission using a fluid to transfer power for bicycles has been considered for some time with a refined practical embodiment using a variable displacement pump and fixed displacement motor to change mechanical advantage in response to pressure changes directly related to changes in rider torque by Sato in the 1990's.
However, this fluid automatic bicycle transmission is not a positive displacement device so diverges from prior art on the method of transferring power using fluids. This transmission applies concepts found among the fluid pump/motors in Class 415, Subclass 89, [Sharpneck 1883, 271139, Budrys 1981, 4251184], along with principles from Class 475, Subclass 94, [Taylor 1935, RE020988] as this fluid automatic bicycle transmission uses drag as the primary means to transfer power, rotation of the outer shell as the functional equivalent to an impeller and wherein a functional equivalent to a stator of vanes and springs can be used to react to rider input torque by altering drag thereby changing mechanical advantage in a limited manner. Using drag as the primary means to transfer power is a crucial difference from prior art in small and fractional horsepower rated transmissions that results in important advantages.
To adapt easily as a replacement part to bicycles and other small horsepower applications using existing bicycle parts the transmission must fit on existing bicycle hubs and especially important of these are the cassette replacement FIG. 5-A, multi-speed freewheel replacement FIG. 5-C, and single-speed freewheel replacement FIG. 5-D, and, any such device must use a basic hollow geometry limited in width by the distance between the hub flange, spokes or rim support, and the frame (see Inset FIG. 1). The hub replacement FIG. 5-E, has the advantages of being less exposed to weather and abrasive road grit and also having cassette type cog replacement, and, all embodiments are fully serviceable using common bicycle industry tools.
For this class of device design focus is on the ability of the transmission to respond to torque with changes in mechanical advantage in a manner that the rider considers automatic transmission operation over varied terrain. Bicycle and other human powered vehicle ridership can be separated into groups by weight and aggressiveness in order to inventory fixed geometry transmissions tuned and adjusted to these groups, or, for racing a method to change spring compression is used, said tuning consisting of appropriate spring and recovery rates, viscosity and maximum flow constraints to allow a practical product to satisfy the variety of human powered transportation needs weather recreational, racing or utility.
A fluid automatic bicycle transmission uses a bicycle crankset with pedals 16c having a single front chainring sprocket 16b, and having a chain 17, all supported by a bicycle frame 21, and having a rear hub 12, having a fluid automatic transmission which is a replacement for existing gearing, said chain can deliver power to a rear sprocket 6, connected using threads or other means to an outer shell 4, of said transmission having a fluid chamber 9, said outer shell separated from an inner shell 1, by a pair of bearings 7a–7b, and sealing means 5a–5b, so that as said outer shell rotates, drag caused by this motion within said fluid chamber accelerates the fluid which accelerates said inner shell by dragging said stator affixed to said inner shell within a closed fluid system to transfer power. The geometry shown in FIG. 2-B illustrates a basic fluid couple device using drag to transfer power. This type of device operates at a higher efficiency than positive displacement devices by having all bearing and seal friction add to output power yet loses a portion of this advantage to heat generation during high step-down conditions, the variance of the human pedal stroke attenuating these heat losses.
Another significant difference from prior art is that a positive displacement pump has a loss of output power from slip and must concern itself with precision seals and tolerances thus increasing cost of manufacture and a loss of efficiency as pressure goes up and as usage wears these surfaces down, whereas for the drag device slip is a means to change mechanical advantage without a significant loss of power for this as pressure being negative or suction, instead losses relate to heat generated by stepping down the ratio, and, said drag device's internal paths need not touch, thus wear is minimal and performance is less affected over time than positive displacement devices. Having these advantages, slip only needed be reduced to a practical level so that the rider perceives “high gear” as minimum slip FIG. 3-B, with a range of change in mechanical advantage ending with what the rider perceives as “low gear” where slip is greatest FIG. 3-B2. The rider's cadence is stepped up by the front chainring sprocket 16b, having more teeth than the rear sprocket 6. As step-down by the transmission increases with applied torque the mechanical advantage is increased until the powered wheel and cadence are approximately 1:1 for a normal “low gear” of said transmission for average cyclists; note that recumbent and many utility human powered vehicles require as low a ratio as 1:2 for “low gear”.
These major differences are derived from rotating the housing 4, [Budrys 1981, 4251184], using drag to transfer power with a fluid, [Sharpneck, 1883, 271139], and then to use torque to change dimensions of the shear zone thus changing drag as the means to change mechanical advantage for the rider without any other rider input for automatic operation while the racing market will demand a means to change how easy it is to get to “low gear” that is rider actuated.
Such automatic devices have distinct performance differences from a chain drive with multiple sprockets, among these is prominent the distinction that as the rider adds more power the mechanical advantage is reduced. As the terrain changes, then, the transmission acts as a torque limiter up to a point, then the transmission becomes a fluid couple and no longer allows any change to mechanical advantage while going up a hill, and, when terrain is nearly level or downhill, the device will change until the minimum slip condition is reached. If there is no hill and the rider adds more power the device reacts after dampening with a lower gear ratio, then as the riders continues to accelerate their high torque eventually becomes less per stroke as the acceleration is reduced and the device automatically compensates this by raising the mechanical advantage; the rider can thus control the mechanical advantage consciously from the way they use changes in torque while pedaling. Therefore, this device while not requiring conscious and perceptive use by the rider can be used by a perceptive rider to change mechanical advantage consciously or intentionally.
At human power ratings the total losses in power transfer for this fluid transmission is very little at low power inputs and approaches 96% efficiency for an average rider losing little to heat generation, yet, if a steady and high torque input is applied the transmission operates at maximum step-down and loses significant energy to heat generation if run for long periods in this manner.
At rates of output typical for casual riders continuous power output is approximately 150-watts with a cadence of 40–60 rpm. Because of this low cadence and power output the clearances of the shear zone and total flow within the device must be limited else there will be too much fluid for the rider to energize and power will not transfer in a practical manner to the inner shell.
FIG. 3 illustrates the change in clearances B1, B2, and B3 between the stator 2, and outer shell 4. To change drag in response to torque, springs 3a, are compressed by flow pressure and drag against the vane 3b, thus increasing the clearance between said vane and said outer shell until fully open where there is a maximum clearance FIG. 3-B, B2, and FIG. 3-C, B2, thus attaining maximum flow and step down or slip this condition being defined as “low gear” for this type of transmission. In FIG. 3-B, B3 is illustrated the stator cross-section along with the fluid chamber formed by the clearances between said stator, vane, sealing means and outer shell, this area perpendicular to the general flow path said flow turbulent and complex.
To best satisfy rider preferences, changes in vane position can be dampened or slowed to relate to human cadence ranges else the mechanical advantage will change instantly and the ratio would go from a higher to a lower ratio and then back for each revolution of the crankarms.
In the mechanical stator (see FIG. 12), the vane 3b, is mounted onto a piston 3c1, which supports said vane and which is structurally attached to said stator body perpendicular to the stator face it is threaded into and directionally towards the flow. The vane is bored for this support piston for said bore to act as a cylinder, said vane body drilled with a small port C11, FIG. 12, and thus the support piston must pump fluid through said port in order for the vane to move being immersed thus dampening any motion said dampening performance tuned by the size and number of ports or restrictions, including flow directional control for asymmetric response so that dampening will be more or less depending on the direction of flow through the dampenng circuit, this all is part of the scope of performance related attributes for any mechanical vane dampening system which are easy to turn by changing viscosity or spring strength or the number of vanes used. For example, five vane positions are illustrated in FIG. 12, yet a small child may only require one vane with light springs while the very large person will require all five vanes with heavy springs. The figures in addition to illustrating a mechanical dampening system 2a, FIG. 4, also illustrate another system that uses a composite stator 2b. 
A composite stator (see FIG. 11), can function similarly to mechanical stators from engineered spring and dampening qualities formed into the materials using plastics, amendments and structural shapes from metallic spring materials, said shapes also affecting drag characteristics by their geometry as it relates to flow paths especially bound vortices which can be manipulated to alter drag. Composite stators offer good economy for performance gained. Due to the slow recovery properties of plastics, vane construction can include metallic springs attached to the stator body before injection molding completes the vane to enhance the ability of the vane to fully recover, thus the stator is a composite using metals and plastics to attain optimum performance. However, plastic vanes without metallic springs are adequate for most utility uses.